Consider the following species:

N^3–, O^2–, F^–, Na⁺, Mg²⁺ and Al³⁺

A. What is common in them?

B. Arrange them in the order of increasing ionic radii.

A. In the given examples of isoelectronic species have a same number of electrons which is equal to 10. Hence, the given species are isoelectronic, i.e.

N^3- has 7+3 = 10 electrons

O^2- has 8+2 = 10 electrons

F^- has 9+1 = 10 electrons

Na⁺ has 11-1 = 10 electrons

Mg²⁺ has 12-2 = 10 electrons

AL³⁺ has 13-3 = 10 electrons

B. As the magnitude of the effective nuclear decreases, the ionic radii of the ions increase.

The following arrangement denotes the elements arranged in the order of increasing nuclear charge:

N^3- < O^2- < F^- < Na⁺ < Mg²⁺ < AL³⁺

Nuclear charge = +7 +8 +9 +11 +12 +13

The following arrangement denotes the elements arranged in the order of increasing ionic radii:

AL³⁺ < Mg²⁺ < Na⁺ < F^- < O^2- < N^3-